A novel strategy for constructing mesoporous solid superbase catalysts: bimetallic Al–La oxides supported on SBA-15 modified with KF

Abstract

Bimetallic Al–La oxides were conjointly precoated on SBA-15 prior to the introduction of potassium fluoride to achieve solid superbases at low temperature by a modified wetness impregnation method. This breaks the tradition of decomposition of KNO₃ at high temperature and gives rise to a new approach to generating superbasic sites on SBA-15. The physico-chemical characteristics of the prepared KF/Al–La@SBA-15 materials were investigated using FT-IR, XRD, TG-DTG, N₂ adsorption–desorption, TEM, SEM-EDS, acid–base titration, Hammett indicators and CO₂-TPD measurements. The results demonstrated that the addition of Al species promoted the dispersion behavior of La species inside the channels, and the bimetallic species could synergistically protect the mesoporous structures of SBA-15 against KF corrosion. With increasing Al content, KF/Al–La@SBA-15 exhibited a long-range ordering of the pores with relatively narrow pore size distribution as well as high specific surface area. The research results showed that the KF/Al–La@SBA-15 (0.4) catalyst possessed a total basicity up to 0.79 mmol g⁻¹ and superbasicity with a strength of 26.5. The catalytic activity of the prepared materials was evaluated in the ring-opening reaction of propylene oxide with methanol. Compared with the SBA-15 supported monometallic oxide (Al or La) catalysts, KF/Al–La@SBA-15 (0.4) exhibited the highest catalytic activity for the ring-opening reaction of propylene oxide with methanol. This is associated with the synergistic effects between Al and La species and the high dispersion of active components on the SBA-15 support.